1. Field of the Invention
This invention relates generally to non-destructive testing of metallic material. More particularly, it relates to analyzing eddy current tests.
The Government has rights in this invention pursuant to Contract No. DE-AC12-76-SN00052 between the U.S. Department of Energy and the General Electric Company.
2. Description of Related Art
In this technology, an eddy current probe senses any flaws in a metallic object. The eddy current probe may be a dual bobbin probe that has two electromagnetic coils which may be operated separately (in an absolute mode) or together (in a differential mode). As the probe is passed over a flaw in the metallic object, the current (eddy current) within the metallic object changes due to the flaw. These current changes within the metallic object are detected as a change in electrical impedance of the probe's coil. The impedance of the coil is then recorded as an electrical signal on a storage device.
Once these electrical signals are stored on the storage device, the signals must be analyzed by a human operator. The human operator bases his analysis on a set of guidelines which guide the operator's analysis. The difficulty of human analysis of eddy current signals is that the guidelines are interpreted in any number of different ways depending on which operator is doing the analysis. In addition, a single operator may be inconsistent in his analysis. This makes comparisons of two separate analyses almost impossible because of the inconsistent nature of the application of the guidelines. An operator also may inadvertently introduce his own bias and beliefs into the analysis process.
In addition, the guidelines are frequently changed as new analysis techniques are developed. The operator must be constantly retrained as new guidelines are created. Also, an operator's sizing of flaws, based on his own visual analysis, is inconsistent from flaw to flaw and analysis to analysis due to human limitations.
The actual analysis done by a human operator, in addition to being inconsistent, is also time consuming and expensive. Much of the analysis requires doing the same steps over and over again until a diagnosis is reached.
The signals generated by the probe are typically displayed on a CRT screen and form visual patterns which are interpreted by an operator. The interpretation of eddy current data can be quite complex as any phenomena which affects the electrical impedance of the probe coil will generate visible patterns. Combinations of these patterns can make interpretation and sizing of a flaw very difficult.
Other computer based systems have been developed which offer automated interpretations of eddy current data. These systems are available from a variety of vendors. However, none of the previous systems emulate a human operator's interpreting process including reasoning with uncertainty and pattern recognition. A substantial body of knowledge is then applied during this interpretation process requiring many factors to be considered. Prior systems that achieve these goals use human operators as the primary interpreters. These generally fail to use all of the pertinent information or impose some bias that makes later comparison subjective.